4,391 research outputs found
Learning a Bias Correction for Lidar-only Motion Estimation
This paper presents a novel technique to correct for bias in a classical
estimator using a learning approach. We apply a learned bias correction to a
lidar-only motion estimation pipeline. Our technique trains a Gaussian process
(GP) regression model using data with ground truth. The inputs to the model are
high-level features derived from the geometry of the point-clouds, and the
outputs are the predicted biases between poses computed by the estimator and
the ground truth. The predicted biases are applied as a correction to the poses
computed by the estimator.
Our technique is evaluated on over 50km of lidar data, which includes the
KITTI odometry benchmark and lidar datasets collected around the University of
Toronto campus. After applying the learned bias correction, we obtained
significant improvements to lidar odometry in all datasets tested. We achieved
around 10% reduction in errors on all datasets from an already accurate lidar
odometry algorithm, at the expense of only less than 1% increase in
computational cost at run-time.Comment: 15th Conference on Computer and Robot Vision (CRV 2018
The lambda-dimension of commutative arithmetic rings
It is shown that every commutative arithmetic ring has -dimension
. An example of a commutative Kaplansky ring with -dimension 3
is given. If satisfies an additional condition then -dim(
Chemical Evolution of the Juvenile Universe
Only massive stars contribute to the chemical evolution of the juvenile
universe corresponding to [Fe/H]<-1.5. If Type II supernovae (SNe II) are the
only relevant sources, then the abundances in the interstellar medium of the
juvenile epoch are simply the sum of different SN II contributions. Both
low-mass (~8-11M_sun) and normal (~12-25M_sun) SNe II produce neutron stars,
which have intense neutrino-driven winds in their nascent stages. These winds
produce elements such as Sr, Y, and Zr through charged-particle reactions
(CPR). Such elements are often called the light r-process elements, but are
considered here as products of CPR and not the r-process. The observed absence
of production of the low-A elements (Na through Zn including Fe) when the true
r-process elements (Ba and above) are produced requires that only low-mass SNe
II be the site if the r-process occurs in SNe II. Normal SNe II produce the CPR
elements in addition to the low-A elements. This results in a two-component
model that is quantitatively successful in explaining the abundances of all
elements relative to hydrogen for -3<[Fe/H]<-1.5. This model explicitly
predicts that [Sr/Fe]>-0.32. Recent observations show that there are stars with
[Sr/Fe]<-2 and [Fe/H]<-3. This proves that the two-component model is not
correct and that a third component is necessary to explain the observations.
This leads to a simple three-component model including low-mass and normal SNe
II and hypernovae (HNe), which gives a good description of essentially all the
data for stars with [Fe/H]<-1.5. We conclude that HNe are more important than
normal SNe II in the chemical evolution of the low-A elements, in sharp
distinction to earlier models. (Abridged)Comment: 10 pages, 9 figures, to appear in Pub. Astron. Soc. Australi
Structural trends and basement rock subdivisions in the western Gulf of St. Lawrence, northern Appalachians
We compiled industry seismic and LTTHOPROBE deep seismic data in the southwestern Gulf of St. Lawrence, and interpreted them together with gravity, magnetic and industry well data, to study the deepest sediments, which are assignable to the Horton Group of Late Devonian-Early Carboniferous age, and the basement rocks of the northern Appalachians.
Three upper crustal basement blocks with differing seismic character and orientation of geological structures were identified. South of the Appalachian structural front and parallel to it, two blocks with a northwest regional strike were interpreted to be allochthonous on Grenvillian crust. The basement block immediately south of the Appalachian structural front (Laurent) shows deformations compatible with Acadian or older northward thrusting, whereas the second (Bradelle) displays north dipping reflections, possibly related to formation of the Magdalen Basin. These basement blocks may contain the offshore extensions of either the Humber or Dunnage Appalachian terranes, or both.
The Catamaran, Fredericton, and Belleisle faults in New Brunswick appear to extend to the northeast across the third basement block (Shediac), parallel to the main structural trends in this block. The Shediac block contains the extensions of the Gander and Avalon terranes, and the deep seismic data suggest that the Gander/Avalon boundary cuts through the entire crust
This compilation enabled us to address the problem of the formation of the Magdalen Basin. Several Horton Group subbasins, bounded by normal faults, indicate a widespread crustal extension phase which coincided with the early development of the Magdalen Basin. Compressive strike-slip movement inferred from the seismic data along the Belleisle Fault suggested that this fault played a major role in the formation of the basin, but crustal stretching occurred in an area not bounded by this fault The overall asymmetry of the Magdalen Basin suggests that dip-slip movement occurred along a fault (the Hollow Fault?) bounding the basin to the east. The existence of a "Canso Fault" at the location proposed by several authors is not supported by our work. A better candidate for its location may be along the Bradelle/Shediac basement block boundary.
RÉSUMÉ
Nous avons compilé les données acquises à l'aide de la sismique industrielle et de la sismique à forte pénétration LTTHOPROBE en provenance du sud-ouest du Golfe du Saint-Laurent, les avons interprété en conjonction avec les données gravitaires, magnétiques et de forage industriel, et ce dans le but d'étudier les sédiments les plus profonds, attribuables au Groupe de Horton d'âge dévonien tardif à carbonifère précoce, ainsi que les roches constituant le socle dans les Appalaches septentrionales.
On identifia trois blocs de socle supracrustaux montrant des configurations sismiques et une orientation des structures géologiques différentes. On interprète comme allochtones stir une croûte grenvillienne deux blocs ayant une direction régionale nord-ouest, situes au sud du front structural appalachien et parallèle les à ce dernier. Le bloc de socle sis juste au sud du front structural appalachien (bloc de Laurent) montre des déformations compatibles avec un chevauchement vers le nord acadien ou plus ancien, alors que l’autre bloc (bloc de Bradelle) présente des réflexions pentées nord et reliées possiblement à la formation du Bassin de la Madeleine. Ces blocs de socle pourraient contenir les extensions vers le large des lanieres appalachiennes de Humber et/ou de Dunnage.
Les failles de Catamaran, de Fredericton et de Belleisle, au Nouveau-Brunswick, semblent se prolonger vers le nord-est par-dela le troisième bloc de socle (bloc de Shediac); elles sont parallèles aux principales tendances structurales à l'intérieur de ce bloc. Le bloc de Shediac contient les prolongements des lanières de Gander et d'Avalon; les données de la sismique à forte pénétration suggèrent que la frontiere Gander/Avalon traverse toute l'ecorce.
Cette compilation nous à permis d'envisager le problème de la formation du Bassin de la Madeleine. Plusieurs petits sous-bassins, appartenant au Groupe de Horton et limites par des failles normales, indiquent une phase répandue d'extension crustale qui coiincida avec l'amorce du Bassin de la Madeleine. Un décrochement en compression, inféré des données sismiques, le long de la Faille de Belleisle suggère que cette faille joua un role majeur dans la formation du bassin bien que retirement crustal survint dans une région non limitée par cette faille. L'asymettie d'ensemble du Bassin de la Madeleine suggère que le mouvement selon le rejet-pente se produisit le long d'une faille (Faille de Hollow?) limitant le bassin a Test. Nos travaux ne confortent pas l'hypothèse d'une "Faille de Canso" à l'endroit avarice1 par phisieurs auteurs. Un meilleur site pour sa localisation serait le long de la frontière entre les blocs de socle de Bradelle et de Shediac.
[Traduit par le journal
Selfduality for coupled Potts models on the triangular lattice
We present selfdual manifolds for coupled Potts models on the triangular
lattice. We exploit two different techniques: duality followed by decimation,
and mapping to a related loop model. The latter technique is found to be
superior, and it allows to include three-spin couplings. Starting from three
coupled models, such couplings are necessary for generating selfdual solutions.
A numerical study of the case of two coupled models leads to the identification
of novel critical points
The 2-D electron gas at arbitrary spin polarizations and arbitrary coupling strengths: Exchange-correlation energies, distribution functions and spin-polarized phases
We use a recent approach [Phys. Rev. Letters, {\bf 84}, 959 (2000)] for
including Coulomb interactions in quantum systems via a classical mapping of
the pair-distribution functions (PDFs) for a study of the 2-D electron gas. As
in the 3-D case, the ``quantum temperature'' T_q of a classical 2-D Coulomb
fluid which has the same correlation energy as the quantum fluid is determined
as a function of the density parameter r_s. Spin-dependent exchange-correlation
energies are reported. Comparisons of the spin-dependent pair-distributions and
other calculated properties with any available 2-D quantum Monte Carlo (QMC)
results show excellent agreement, strongly favouring more recent QMC data. The
interesting novel physics brought to light by this study are: (a) the
independently determined quantum-temperatures for 3-D and 2-D are found to be
approximately the same, (i.e, universal) function of the classical coupling
constant Gamma. (b) the coupling constant Gamma increases rapidly with r_s in
2-D, making it comparatively more coupled than in 3-D; the stronger coupling in
2-D requires bridge corrections to the hyper- netted-chain method which is
adequate in 3-D; (c) the Helmholtz free energy of spin-polarized and
unpolarized phases have been calculated. The existence of a spin-polarized 2-D
liquid near r_s = 30, is found to be a marginal possibility. These results
pertain to clean uniform 2-D electron systems.Comment: This paper replaces the cond-mat/0109228 submision; the new version
include s more accurate numerical evaluation of the Helmholtz energies of the
para- and ferromagentic 2D fluides at finite temperatures. (Paper accepted
for publication in Phys. Rev. Lett.
Étude exploratoire des caractéristiques professionnelles d'un échantillon de suicidants hospitalisés
Cette étude a pour objectif de décrire les caractéristiques professionnelles d’un échantillon de suicidants. Un enquêteur a interrogé les suicidants âgés de 18 à 65 ans, hospitalisés consécutivement dans une unité spécialisée du CHU d’Angers sur une durée de 6 mois et demi. Au total, 87 suicidants actifs avec un emploi ont été interrogés. Ils ont souvent été confrontés à des contraintes organisationnelles décrites dans la littérature comme responsables de souffrance mentale liée au travail. Cela concerne globalement autant les hommes que les femmes. En comparaison aux enquêtes de santé au travail (Sumer, Samotrace…), les suicidants sont plus nombreux à ressentir entre autres un stress intense au travail, une conscience professionnelle heurtée et à être en situation tendue selon le modèle de Karasek. Cela pourrait être en faveur d’un lien entre les tentatives de suicide et certains facteurs de pénibilité mentale au travail. Les résultats de cette étude sont à interpréter avec prudence du fait des phénomènes de circularité des données et de la faiblesse de l’échantillon
Vlasov moment flows and geodesics on the Jacobi group
By using the moment algebra of the Vlasov kinetic equation, we characterize
the integrable Bloch-Iserles system on symmetric matrices
(arXiv:math-ph/0512093) as a geodesic flow on the Jacobi group. We analyze the
corresponding Lie-Poisson structure by presenting a momentum map, which both
untangles the bracket structure and produces particle-type solutions that are
inherited from the Vlasov-like interpretation. Moreover, we show how the Vlasov
moments associated to Bloch-Iserles dynamics correspond to particular subgroup
inclusions into a group central extension (first discovered in
arXiv:math/0410100), which in turn underlies Vlasov kinetic theory. In the most
general case of Bloch-Iserles dynamics, a generalization of the Jacobi group
also emerges naturally.Comment: 45 page
Negative differential resistance in nanotube devices
Carbon nanotube junctions are predicted to exhibit negative differential
resistance, with very high peak-to-valley current ratios even at room
temperature. We treat both nanotube p-n junctions and undoped
metal-nanotube-metal junctions, calculating quantum transport through the
self-consistent potential within a tight-binding approximation. The undoped
junctions in particular may be suitable for device integration.Comment: 4 pages, 4 figures, to appear in Physical Review Letter
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